Significant advances in industrial process control technology have vastly improved all aspects of factory and plant operation. Before the introduction of today's modem industrial process control systems, industrial processes were operated/controlled by humans and rudimentary mechanical controls. As a consequence, the complexity and degree of control over a process was limited by the speed with which one or more people could ascertain a present status of various process state variables, compare the current status to a desired operating level, calculate a corrective action (if needed), and implement a change to a control point to affect a change to a state variable.
Improvements to process control technology have enabled vastly larger and more complex industrial processes to be controlled via programmed control processors. Control processors execute control programs that read process status variables, execute control algorithms based upon the status variable data and desired set point information to render output values for the control points in industrial processes. Such control processors and programs support a substantially self-running industrial process (once set points are established).
Notwithstanding the ability of industrial processes to operate under the control of programmed process controllers at previously established set points without intervention, supervisory control and monitoring of control processors and their associated processes is desirable. Such oversight is provided by both humans and higher-level control programs at an application/human interface layer of a multilevel process control network. Such oversight is generally desired to verify proper execution of the controlled process under the lower-level process controllers and to configure the set points of the controlled process.
Data access servers facilitate placing process control data within reach of a variety of higher-level monitoring/control client applications. During the course of operation, process controllers generate status and control information concerning associated processes. The controllers' process status and control information is stored within process control databases and/or distributed to a number of locations within the process control network. Other process information is generated/stored within field devices (e.g., intelligent transmitters) having digital data communication capabilities. The process information is retrieved from the databases and field devices by data servers for further processing/use by the process control system. For example, the data access servers provide the retrieved information to a variety of client applications providing high-level control and monitoring (both human and computerized) services.
Proper operation of the high-level control and monitoring applications relies upon proper data interfaces between the process control/field device levels of a process control system and the higher-level supervisory/monitoring levels. The raw data at the control/field device levels of a process control system is stored in a variety of formats depending upon standards incorporated into the process control systems. Likewise, the client applications associated with, for example, the supervisory and monitoring level of a process control system potentially receive data from the data access servers according to any one (or more) of multiple existing (and future) application data interface protocols.
There are presently many different supervisory-level client applications that rely upon data provided by lower level components of a process control system. The supervisory-level client applications access/share the process data via known industry standard protocols such as dynamic data exchange (DDE), SuiteLink (transport protocol of WonderWare Corporation, 100 Technology Dr., Irvine, Calif.), and OPC (OLE for Process Control). The known supervisory level client applications not only encapsulate the logic/processes involved in extracting the process data from field devices, but also the implementation of the client communication for retrieving/receiving the data. This relatively static, limiting approach to client application implementation leads to duplication/replication of effort (a distinct version of client application for extracting device data is created for each communication standard that may be used to retrieve that data). This approach also creates an inability of data access server developers to leverage prior server versions. Users were slow in migrating from existing client applications to new client applications incorporating more effective protocols developed over the years due to incompatibilities with existing data provider communication protocols.
In view of the limitations of known data access servers, especially with regard to extensibility to provide data according to new, or previously unsupported, client application data access protocols, a more easily extended/modified data access server is desired.